Improved production of levoglucosan and levoglucosenone from acid-impregnated cellulose via fast pyrolysis

Cellulose - In this research, the production of levoglucosan (LG) and levoglucosenone (LGO) was improved from acid-impregnated cellulose via fast pyrolysis. Thermogravimetric and kinetic analysis...     

A convenient catalytic approach to synthesize straight boron nitride nanotubes using synergic nitrogen source

Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO₂)₂ · H₂O, NH₄Cl, NaN₃ and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to 5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed.     

Design optimization of guide vane for mitigating elbow erosion using computational fluid dynamics and response surface methodology

A 90° elbow equipped with guide vanes was developed with the intent of reducing elbow erosion.Numer-ical models were formed to predict the maximum erosion rate ...     

基于晶格氧的甲烷化学链重整制合成气

利用氧载体中的晶格氧代替分子氧进行的甲烷化学链重整制合成气,是一种新颖的甲烷制合成气技术,具有较高经济效益和环境效应。它具有省却纯氧设备、能自热、合适的氢碳比、有用的副产物以及过程易于工业化等优点,因此受到国内外研究者的普遍关注。本文介绍了化学链重整技术的基本原理及其特点;重点总结了用于甲烷化学链重整的单金属氧载体和复合金属氧载体的研究进展;同时,探讨了几种具有典型代表的甲烷化学链重整反应装置,并指出串行流化床反应器是实现化学链重整技术工业化最有效的装置;最后对化学链重整技术的拓展应用以及与其他技术交叉运用等发展趋势进行了展望。     

冻土水热力耦合作用的数学模型及数值模拟

将冻土体视为空间弹性体,提出了土体在冻结过程中水分场、温度场、应力场三场耦合的一般数学模型,并给出了相应的离散方程及其解法,最后给出了数值算例,并与实测值比较,证明了该模型和算法的正确性。     

PbSe-MnSe纳米复合热电材料的微结构和电热输运性能

相比于常见的热电材料PbTe, 另一种硫族铅化合物PbSe具有熔点高、Se储量更丰富等优势, 从而越来越受到科学界的关注. 本文采用熔融淬火结合快速热压烧结工艺制备了Pb_0.98-xMn_xNa_0.02Se(0 ≤x ≤ 0.12)纳米复合热电材料, 系统地研究了不同Mn含量对材料微纳结构、机械性能和热电性能的影响规律. 发现纳米复合样品中有面心立方结构的MnSe球状和薄层状析出物, 显微硬度得到显著增强. 少量固溶的Mn增加了能带简并度, 使功率因子提高, 球状析出物使声子散射增强、热导率降低, 体系的热电优值ZT得到优化; 但是当Mn含量更高时, 赛贝克系数趋于饱和, 连续析出物使晶格热导率反常增大, ZT 没有得到进一步改善. 通过进一步调节Na含量优化了载流子浓度, 获得了ZT=0.65的PbSe-MnSe纳米复合热电材料.     

Crack tip superblunting: experiment,theory and numerical simulation

Experimental revelation ofsuperblunting along plane strain predominant crack tip segment is reported here for modified polyproplene. As elucidated by a heuristic model of progressive circumferential cold-draw, the formation of superblunting crack tip depends critically on the ratio between the cold-draw propagation speed and the loading speed, and contributes significantly to the material toughening, especially for the improvement in impact toughness. Detailed numerical calculations are conducted based on a hyperelastic-viscoplastic and anisotropic damage constitutive model at finite deformation. The simulated results recapitulate the essential features of crack tip superblunting. The project supported by the National Natural Science Foundation of China     

煤系高岭土的DTA特征

利用程序升温热分析法得到煤系高岭土在不同气氛下的ＴＧ／ＤＴＡ谱图。通过比较煤系高岭土与普通高岭土的ＴＧ／ＤＴＡ谱图，可以发现：在惰性气氛下煤系高岭土的ＤＴＡ谱图与普通高岭土的谱图基本一致；而在空气气氛下，由于煤的燃烧反应致使煤系高岭土的吸热谷被部分或全部遮盖，另外在３００℃左右有弱的放热峰出现。比较煤系高岭土与普通高岭土的吸热谷特征可以得出煤系高岭土的结构完整性与结晶度较差。     

Selective production of levoglucosenone by catalytic pyrolysis of cellulose mixed with magnetic solid acid

Cellulose - In this study, magnetic solid acid Fe3O4/C–SO3H600 was synthesized and applied in catalytic fast pyrolysis of cellulose for the selective production of levoglucosenone (LGO). The...